Fig. 7: Effect of SFB growth in a heterologous host on tip morphology.

a–e Mouse-SFB morphological stages, when SFB was grown in rats, equivalent to those identified at the tip of mouse-SFB colonizing mice. a–c/e(i), Representative tomographic slices from reconstructed tomograms showing SFB tip of stages: 1 (EMD-52700), 2 (EMD-52701), 3 (EMD-52702) and 5 (EMD-52703). d(i) Representative projection image showing SFB tip of stage 4. The selected representative SFB from stages 1–5 have a length of 2.1, 2.3, 1.6, 8.2, and 3.7 µm. a–e(ii) Close-ups of the SFB tip shown in (a–e(i)). f Length of mouse-SFB grown in rats (n = 79) from 4 independent experiments assigned to each tip stage, including filaments where no distinction could be made between stage 4 and 5. The statistical significance was assessed using the Kruskal–Wallis test followed by a Dunn’s test correction for multiple comparisons (stage 1 vs. 5, p = 0.0006; stage 2 vs. 5, p < 0.0001; stage 3 vs. 5. p = 0.0181, stage 1 or 2 vs. stage 4/5, p < 0.0001; stage 3 vs. 4/5, p = 0.0027). Length of the tip of mouse-SFB g IOs and h filaments analysed. Length of corresponding SFB i IOs and j filaments used for tip length analysis of SFB grown in mice and rats. IOs between 2 and 2.4 µm of length were included in the analysis (n = 27 IOs in mice, n = 38 IOs in rats). Filaments below 20 µm length were included in the analysis (n = 39 filaments in mice and n = 10 filaments in rats). The statistical significance was assessed using an unpaired two-sided t-test for (g, i) (g: p = 0.0004, i: ns: not significant) and using a two-sided Mann–Whitney U test for (h, j) (h: p = 0.0087, j: ns: not significant). For f–j individual measurements and the corresponding mean are shown. Representative projection images of mouse-SFB (mSFB) filaments (FIL) grown in k mice and l rats. The tip length measurement is shown by a white line. m Proportions of IOs assigned to Stages 1-3 when grown (m(i)) in mice and (m(ii)) in rats. n Comparison of the proportions of Stage 2 IOs of mouse-SFB grown in mice (n = 33) and in rats (n = 51). The statistical significance was assessed using a two-sided Fisher’s exact test (Stage 2 in mice vs in rats, p = 0.0147). Source data are provided as a Source Data file for (f–j, m, n). The same data were used to prepare (m, n). Scale bars: a–e(i), k, l: 50 nm; a–e(ii): 20 nm.